Photons in coupled microsphere resonators

Microsphere resonators doped with semiconductor nanocrystals are explored as building blocks for coupled-resonator optical waveguides (CROWs). The evolution of individual resonator modes into coherently coupled waveguide modes is studied using imaging spectroscopy and polarization-sensitive mode mapping. Photon mode coupling is evidenced by the measured mode splittings and emission intensity distributions along the coupled microsphere structure. The observed modifications in both mode splitting and field intensity between odd and even resonator constituents are explained in the frame of a simple coupled-oscillator model. With increasing coupling strength the level splitting increases and the oscillator strength becomes redistributed among the different coupled microsphere states. For each resonator constituent of a six-sphere system a specific mode splitting spectrum is found, in agreement with theoretical predictions.